Police cars were seen parked in front of Carriage Gates – one of the most prominent entrances to the Palace of Westminster – following the incident on Tuesday afternoon.
A man wearing a red hooded top was seen handcuffed and surrounded by police.
The area was cordoned off during the incident and the entrance was closed.
A spokesperson for UK Parliament: “We are aware of an incident outside Carriage Gates. Parliamentary Security and the Metropolitan Police are present and managing the situation.”